Water heater appliance

ABSTRACT

A heat pump water heater and a method for controlling a relative humidity in an environment including the heat pump water heater are provided. The heat pump water heater includes an evaporator, a condensate collection tray, and a condensate pump for discharging collected condensate. Notably, the amount of condensate collected correlates to the humidity level in the environment. Therefore, an exemplary method contemplates determining an average operating value of the condensate pump, the average operating value being a function of the pump operating time and the condensate pump rate. Based on the temperature of the environment and the average operating value, the relative humidity may be determined and the operation of the heat pump water heater may be adjusted to regulate the relative humidity.

FIELD OF THE INVENTION

The present subject matter relates generally to heat pump water heater appliances.

BACKGROUND OF THE INVENTION

Heat pump water heaters are gaining broader acceptance as a more economic and ecologically-friendly alternative to electric water heaters. These systems utilize a condenser configured in a heat exchange relationship with a water storage tank, for example wrapped around the tank in a series of coils. During operation of the vapor compression heat pump cycle, air flows across an evaporator and transfers energy to a refrigerant flowing through the evaporator. As such, the refrigerant exits the evaporator as a superheated vapor and/or high quality vapor mixture. Upon exiting the evaporator, the refrigerant enters a compressor where the pressure and temperature increase and the refrigerant becomes a superheated vapor. The superheated vapor from the compressor then enters the condenser, wherein the superheated vapor transfers energy to the water within a storage tank and returns to a saturated liquid and/or high quality liquid vapor mixture.

As heat is absorbed from the air flowing over the evaporator, condensation forms which must be collected and discharged. Thus, certain heat pump water heaters include a condensate pump for discharging collected condensate to an external drain. In addition to absorbing heat energy during operation of the heat pump water heater, the evaporator may be used to help control the relative humidity of an environment in which the heat pump water heater is located. In order to effectively control the relative humidity within the environment, it is first desirable to measure the humidity level in that environment. Additional sensors, such as a humidity sensor, may be included in the environment for determining humidity, but such sensors add costs and require extra space.

Accordingly, a heat pump water heater appliance with features for measuring the relative humidity of the ambient environment would be useful. More specifically, a heat pump water heater appliance having an integral means for measuring and regulating relative humidity without requiring additional parts would be particularly beneficial.

BRIEF DESCRIPTION OF THE INVENTION

The present disclosure provides a heat pump water heater and a method for controlling a relative humidity in an environment including the heat pump water heater. The heat pump water heater includes an evaporator, a condensate collection tray, and a condensate pump for discharging collected condensate. Notably, the amount of condensate collected correlates to the humidity level in the environment. Therefore, an exemplary method contemplates determining an average operating value of the condensate pump, the average operating value being a function of the pump operating time and the condensate pump rate. Based on the temperature of the environment and the average operating value, the relative humidity may be determined and the operation of the heat pump water heater may be adjusted to regulate the relative humidity. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In a first exemplary embodiment, a method for controlling a relative humidity in an environment including a heat pump water heater is provided. The heat pump water heater includes a compressor, a condenser, and an evaporator. The method includes determining an average operating value of a condensate pump of the heat pump water heater, the condensate pump being in fluid communication with a condensate collection tray for discharging condensate collected from the evaporator of the heat pump water heater. The method further includes determining a temperature of the environment and determining, based on the average operating value and the temperature of the environment, the relative humidity of the environment. An operating parameter of the heat pump water heater is adjusted to regulate the relative humidity of the environment.

In a second exemplary embodiment, a water heater appliance defining a vertical direction if provided. The water heater appliance includes an evaporator being configured to absorb heat and produce condensate and a condensate collection tray disposed under the evaporator along the vertical direction and being configured for collecting the condensate from the evaporator. A condensate pump is in fluid communication with the condensate collection tray, the condensate pump being configured for discharging the condensate from the condensate collection tray through a condensate discharge line. A controller for controlling a relative humidity in an environment in which the water heater appliance is located is configured for determining an average operating value of the condensate pump and determining a temperature of the environment. Based on the average operating value and the temperature of the environment, the relative humidity of the environment is determined, and an operating parameter of the heat pump water heater is adjusted to regulate the relative humidity of the environment.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.

FIG. 1 provides a front elevation view of a water heater appliance according to an exemplary embodiment of the present disclosure.

FIG. 2 provides a front section view of the exemplary water heater appliance of FIG. 1.

FIG. 3 provides a perspective view of a machinery compartment of the exemplary water heater appliance of FIG. 1, with a protective shroud and other components removed for clarity.

FIG. 4 illustrates a method for controlling the relative humidity of an environment including a heat pump water heater according to an exemplary embodiment of the present subject matter.

FIG. 5 provides a plot illustrating the relationship between an average operating value of a condensate pump, the ambient temperature, and the relative humidity according to an exemplary embodiment of the present subject matter.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 provides a front elevation view of a water heater appliance 100 according to an exemplary embodiment of the present disclosure. The water heater appliance 100 defines a vertical direction V, and the water heater appliance 100 extends longitudinally between a top portion 102 and a bottom portion 104 along the vertical direction V. The water heater appliance 100 includes an outer shell or casing 106. The casing 106 generally surrounds a tank 108 (FIG. 2) such that the tank 108 is disposed within the casing 106. The tank 108 includes a top portion 110 and a bottom portion 112 spaced apart from one another along the vertical direction V. In addition, the tank defines an interior volume 114 extending between the top portion 110 and the bottom portion 112 along the vertical direction V.

The casing 106 may be formed from a variety of components. As illustrated, the casing 106 may include a wrapper 116, one or more covers, such as a top cover 118 and a bottom cover 120, and a shroud 122 as illustrated. The shroud 122 may be positioned at the top portion 110 of the tank 108 along the vertical direction V such that the shroud 122 defines a chamber 124 (FIG. 3) positioned over the tank 108 along the vertical direction V. According to the illustrated embodiment, chamber 124 serves as a machinery compartment for housing various operating components of water heater appliance 100. Additionally, the shroud 122 may define a one or more vents or apertures (not shown) that extend through the shroud 122 from or to the chamber 124 of the shroud 122.

Upper and lower heating elements 130, 132 (FIG. 2) and a sealed system 134 (FIG. 2) may also be positioned within the casing 106 for heating water within the tank 108. The upper and lower heating elements 130, 132 can be any suitable heating elements. For example, the upper heating element 130 and/or lower heating element 132 may be an electric resistance element, a microwave element, an induction element, or any other suitable heating element or combination thereof. The lower heating element 132 may also be a gas burner. As will be understood by those skilled in the art and as used herein, the term “water” includes purified water and solutions or mixtures containing water and, e.g., elements (such as calcium, chlorine, and fluorine), salts, bacteria, nitrates, organics, and other chemical compounds or substances.

The water heater appliance 100 also includes an inlet or cold water conduit 136 and an outlet or hot water conduit 138 that are both in fluid communication with a chamber or interior volume 114 (FIG. 2) defined by the tank 108. As an example, cold water from a water source, e.g., a municipal water supply or a well, can enter the water heater appliance 100 through the cold water conduit 136. From the cold water conduit 136, such cold water can enter the interior volume 114 of the tank 108 wherein the water is heated with heating elements 130, 132 and/or sealed system 134 to generate heated water. Such heated water can exit the water heater appliance 100 at the hot water conduit 138 and, e.g., may be supplied to a bath, shower, sink, or any other suitable feature.

As mentioned above, the water heater appliance 100 extends longitudinally between the top portion 102 and the bottom portion 104 along the vertical direction V. Thus, the water heater appliance 100 is generally vertically oriented. The water heater appliance 100 can be leveled, e.g., such that the casing 106 is plumb in the vertical direction V, in order to facilitate proper operation of the water heater appliance 100. It should be understood that the water heater appliance 100 is provided by way of example only and that the present subject matter may be used with any suitable water heater appliance, including for example any heat pump water heater appliance.

FIG. 2 provides a front section view of the water heater appliance 100. As may be seen in FIG. 2, the water heater appliance 100 includes the sealed system 134 for heating water within the interior volume 114 of the tank 108. The sealed system 134 generally operates in a heat pump cycle. Thus, the water heater appliance 100 is commonly referred to as a “heat pump water heater appliance.” The water heater appliance 100 may additionally include one or more auxiliary heating elements, such as the upper heating element 130 and/or the lower heating element 132.

The sealed system 134 may include a compressor 140, a condenser 142 and an evaporator 144. The compressor 140 and/or evaporator 144 of the sealed system 134 may be disposed within the casing 106 at the top portion 102 of the water heater appliance 100, e.g., within the machinery compartment or shroud 122. As is generally understood, various conduits may be utilized to flow refrigerant between the various components of the sealed system 134. Thus, e.g., the evaporator 144 may be between and in fluid communication with the condenser 142 and the compressor 140. During operation of the sealed system 134, refrigerant may flow from the evaporator 144 through the compressor 140. For example, refrigerant may exit the evaporator 144 as a fluid in the form of a superheated vapor and/or high quality vapor mixture. Upon exiting the evaporator 144, the refrigerant may enter the compressor 140. The compressor 140 may be operable to compress the refrigerant. Accordingly, the pressure and temperature of the refrigerant may be increased in the compressor 140 such that the refrigerant becomes a superheated vapor.

The condenser 142 may be assembled in a heat exchange relationship with the tank 108 in order to heat water within the interior volume 114 of the tank 108 during operation of the sealed system 134. In particular, the condenser 142 may be positioned downstream of and in fluid communication with the compressor 140, and may be operable to heat the water within the interior volume 114 using energy from the refrigerant. For example, the superheated vapor from the compressor 140 may enter the condenser 142 wherein it transfers energy to the water within the tank 108 and condenses into a saturated liquid and/or liquid vapor mixture.

The sealed system 134 may also include a throttling device 146 between the condenser 142 and the evaporator 144. Refrigerant, which may be in the form of high quality/saturated liquid vapor mixture, may exit the condenser 142 and travel through the throttling device 146 before flowing through the evaporator 144. The throttling device 146 may generally expand the refrigerant, lowering the pressure and temperature thereof. The refrigerant may then be flowed through the evaporator 144.

The throttling device 146 may be any suitable components for generally expanding the refrigerant. For example, in some exemplary embodiments, the throttling device 146 may be a Joule-Thomson expansion valve, also known as a “J-T valve.” In other exemplary embodiments, throttling device 146 may be an ejector. In still other exemplary embodiments, an electronic expansion valve, a capillary tube, a fixed orifice, or any other suitable apparatus may be utilized as throttling device 146.

The water heater appliance 100 may additionally include a tank temperature sensor 148. The tank temperature sensor 148 may be configured for measuring a temperature of water within the interior volume 114 of the tank 108. The tank temperature sensor 148 can be positioned at any suitable location within the water heater appliance 100. For example, the tank temperature sensor 148 may be positioned within the interior volume 114 of the tank 108 or may be mounted to the tank 108 outside of the interior volume 114 of the tank 108. The tank temperature sensor 148 may further be positioned within an upper portion of the tank 108. Alternatively, the tank temperature sensor 148 may be positioned within a lower portion of the tank 108. When mounted to the tank 108 outside of the interior volume 114 of the tank 108, the tank temperature sensor 148 can be configured for indirectly measuring the temperature of water within the interior volume 114 of the tank 108. For example, the tank temperature sensor 148 can measure the temperature of the tank 108 and correlate the temperature of the tank 108 to the temperature of water within the interior volume 114 of the tank 108. The tank temperature sensor 148 may be any suitable temperature sensor. For example, the tank temperature sensor 148 may be a thermocouple, a thermistor, or a resistance temperature detector.

In addition, water heater appliance 100 may additionally include an air temperature sensor 150. The air temperature sensor 150 may be configured for measuring a temperature of ambient air within the environment in which water heater appliance 100 is located. The air temperature sensor 150 can be positioned at any suitable location within or around water heater appliance 100. For example, the air temperature sensor 150 may be positioned at an inlet of evaporator 144, within chamber 124, or outside casing 106. As will be described in more detail below, according to some embodiments, air temperature sensor 150 may be used for determining the relative humidity of the ambient environment. The air temperature sensor 150 may be any suitable temperature sensor. For example, the air temperature sensor 150 may be a thermocouple, a thermistor, or a resistance temperature detector.

The water heater appliance 100 may further include a controller 154 that regulates operation of the water heater appliance 100. The controller 154 may be, for example, in operative communication with sealed system 134 (such as compressor 140, and/or other components thereof), auxiliary heating elements 130, 132, and/or tank temperature sensor 148. Thus, the controller 154 can selectively activate the sealed system 134 and/or auxiliary heating elements 130, 132 in order to heat water within interior volume 114 of tank 108.

The controller 154 includes memory and one or more processing devices such as microprocessors, CPUs or the like, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with operation of water heater appliance 100. The memory can represent random access memory such as DRAM, or read only memory such as ROM or FLASH. The processor executes programming instructions stored in the memory. The memory can be a separate component from the processor or can be included onboard within the processor. Alternatively, the controller 154 may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software.

During operation of water heater appliance, evaporator 144 is generally configured to absorb heat, e.g., to increase the temperature of the refrigerant. As a result, condensation forms on evaporator 144. For example, condensation may form as a result of latent heat released by the water vapor in the ambient air that is passed through evaporator 144. In addition, the relative humidity of the air passed through evaporator 144 is decreased as the air is cooled by the coils of evaporator 144 and condensate is formed. As described in more detail below, the apparatus and methods discussed herein provide a useful method of using water heater appliance 100, e.g., evaporator 144, for measuring and regulating the relative humidity of an environment.

Referring now to FIG. 3, a drain pump assembly 160 that may be used for collecting and discharging condensate from water heater appliance 100 will be described. More specifically, FIG. 3 provides a close-up, perspective view of a machinery compartment of chamber 124 of water heater appliance 100. Although drain pump assembly 160 is described herein as being configured for use in water heater appliance 100, it should be appreciated that drain pump assembly 160 may be used in any other suitable water heating appliance.

Drain pump assembly 160 generally includes a condensate collection tray 162 and a drain pump 164, each of which will be described below according to an exemplary embodiment of the present subject matter. According to the illustrated embodiment, condensate collection tray 162 is positioned below evaporator 144 of water heater appliance 100 along the vertical direction V. As condensate forms on evaporator 144, it falls into condensate collection tray 162 where it is collected and prevented from falling into chamber 124 or over casing 106. By collecting the condensate, it may be discharged to a suitable drain, such as external drain 166.

According to an exemplary embodiment, condensate collection tray 162 may define a discharge port 170 through which condensate may be pumped by drain pump 164 to external drain 166. As illustrated, drain pump 164 is positioned outside condensate collection tray 162 and includes a pump inlet 172 in fluid communication with condensate collection tray 162. In this regard, drain pump 164 is configured for drawing out and discharging condensate from condensate collection tray 162 through a condensate discharge line 174. According to one embodiment, condensate collection tray 162 may be sloped or can define a low region for collecting condensate near pump inlet 172. In order to prevent backflow of condensate into the condensate collection tray 162, drain pump assembly 160 may further include a check valve 176 positioned on condensate discharge line 174. Any suitable type of check valve or one-way valve may be used to stop the backflow and check valve 176 may be placed at any suitable location downstream of pump inlet 172.

Although drain pump 164 is illustrated as being positioned outside condensate collection tray 162 and outside of chamber 124 and shroud 122, according to alternative embodiments, drain pump 164 could be positioned in any other suitable location where it is in fluid communication with condensate collection tray 162. For example, according to alternative embodiments, drain pump 164 may be located within shroud 122 and may be mounted directly to condensate collection tray 162. Thus, pump inlet 172 draws condensate directly from condensate collection tray 162 and discharges to external drain 166. In this regard, condensate discharge line 174 may be routed through discharge port 170, or discharge port 170 may be plugged or removed and condensate discharge line 174 may extend up out of condensate collection tray 162 and through shroud 122. Other configurations for condensate collection tray 162, drain pump 164, and condensate discharge configurations in general are possible and within the scope of the present subject matter.

According to the illustrated exemplary embodiment, drain pump 164 is a peristaltic pump mounted to the outside of water heater 100 by discharge port 170. However, it should be appreciated that drain pump 164 may be any suitable type of fluid pump having any size, configuration, or position suitable for drawing condensate from condensate collection tray 162 and discharging it through condensate discharge line 174.

According to an exemplary embodiment, drain pump assembly 160 may further include a condensate level sensor 180 that is generally configured for measuring a level of condensate within condensate collection tray 162. Condensate level sensor 180 may be operably coupled with controller 154 to provide an indication of when condensate needs to be discharged from condensate collection tray 162. Condensate level sensor 180 may be any suitable type of water level sensor, such as a float sensor, a capacitive sensor, an optical sensor, a reed switch, etc.

The present disclosure is further directed to methods 200 for operating water heater appliances. Method 200 can be used to operate any suitable water heater system or water consuming appliance. For example, method 200 may be utilized to operate water heater appliance 100 (FIGS. 1 and 2). In this regard, for example, controller 154 may be programmed to implement method 200 and the various steps thereof as discussed herein. However, it should be appreciated that aspects of method 200 may be used to operate any suitable water heating appliance and to measure and regulate relative humidity in an environment.

Referring now specifically to FIG. 4, method 200 may be used for controlling the relative humidity in an environment including a heat pump water heater, such as water heater appliance 100 described above. Method 200 includes, at step 210, determining an average operating value of a condensate pump of the heat pump water heater. As explained above, the condensate pump may be in fluid communication with a condensate collection tray for discharging condensate collected from the evaporator of the heat pump water heater.

As used herein, “average operating value” may refer to a measure of the frequency and magnitude of operation of the condensate pump. According to one exemplary embodiment, determining the averaging operating value includes determining an operating time and a condensate pump rate of the condensate pump during a predetermined time interval. For example, according to one embodiment, the average operating value is the operating time multiplied by the condensate pump rate over the predetermined time interval. The predetermined time may be, for example, one hour, several hours, one day, or any other suitable time period. Thus, for example, using water heater appliance 100 as an example, controller 154 may monitor the operation of drain pump 164 over predetermined period of time, e.g., eight hours. In this regard, the condensate pump rate over that predetermined period of time or an average pump rate over that time period is multiplied by the period of time the drain pump 164 is actually operating to determine the average operating value.

Method 200 further includes, at step 220, determining a temperature of the environment in which the heat pump water heater is located. The temperature of the environment may be measured at an inlet of the evaporator or outside of the heat pump water heater. According to another exemplary embodiment, the temperature of the environment is measured both at an inlet of the evaporator and outside of the heat pump water heater. In such a case, the temperatures may be averaged to determine an accurate temperature of the ambient environment. For example, using water heater appliance 100 as an example, the temperature of the environment may be measured using the air temperature sensor 150. According to alternative embodiments, any suitable temperature sensor may be used placed in any suitable location in or around water heater appliance 100 or within the surrounding environment.

Method 200 further includes, at step 230, determining, based on the average operating value (determined at step 210) and the temperature of the environment (determined at step 220), the relative humidity of the environment. Notably, the average operating value corresponds to the relative humidity in the ambient surrounding environment in which the water heater appliance is located. More specifically, referring to FIG. 5, the relationship between the average operating value of a condensate pump, the ambient temperature, and the relative humidity in an ambient environment is illustrated. This plot illustrates the relationship between the average operating value and the relative humidity of the ambient environment at two ambient air temperatures, e.g., 70 degrees Fahrenheit and 100 degrees Fahrenheit. However, it should be appreciated that the relationship between the average operating value and the relative humidity of the ambient environment may be determined for any ambient air temperature. Although the relationship between the average operating value of a condensate pump, the ambient temperature, and the relative humidity is described above as being determined using FIG. 5, it should be appreciated that other methods of determining the relative humidity are possible and within the scope of the present subject matter. For example, the relationship may be established in a look-up table, defined by a mathematical equation, etc.

In this manner, using the relationship illustrated in FIG. 5, by monitoring the average operating value (determined at step 210) and the temperature of the environment (determined at step 220), the relative humidity of the ambient environment may be determined without requiring additional expensive humidity sensors. For example, for a given ambient temperature, a water heater appliance operating in a more humid environment will generate more condensate, and thus result in a higher average operating value of the condensate pump. By contrast, if the environment has relatively low humidity, less condensate and a lower average operating value will result.

According to an exemplary embodiment, method 200 further includes, at step 240 adjusting an operating parameter of the heat pump water heater to regulate the relative humidity of the environment. In this regard, for example, controller 154 may be programmed to take remedial action if the relative humidity (determined at step 230) exceeds some predetermined threshold. Any suitable operating parameter of water heater appliance 100 or sealed system 134 may be adjusted to regulate the humidity in the environment.

According to one embodiment the adjusted operating parameter is a speed of the compressor of the heat pump water heater. In this regard, increasing the speed of the compressor may increase the rate at which condensate is produced, the rate at which the ambient air is dehumidified, and the condensate pump rate. According to an alternative embodiment, the adjusted operating parameter is a cycle time of the heat pump water heater. In this regard, a longer cycle time of the sealed system results in more dehumidification of ambient air and increases condensate collection. According to another embodiment, the air flow across the evaporator may be reduced to lower the average temperature of the evaporator which will increase the extraction of latent heat through condensation of water vapor versus otherwise sensible heat extracted from the air. According to still another embodiment, the evaporator fan speed and the compressor speed may remain constant, and the electronic expansion valve may be manipulated to allow refrigerant flow at a higher rate, thus lowering the average evaporator temperature which will raise the ratio of latent heat extraction due to water vapor condensation versus sensible heat extraction from the air.

The water heater appliance and method of operation described above provide an integrated and effective means for measuring and regulating relative humidity within an environment in which the water heater appliance is located. The method achieves humidity regulation without the need for additional costly sensors or controllers. It should be appreciated that aspects of water heater appliance 100 described herein are used only for the purpose of explaining aspects of the present subject matter. Other configurations are possible and within the scope of the present subject matter.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A method for controlling a relative humidity in an environment including a heat pump water heater, the heat pump water heater comprising a compressor, a condenser, and an evaporator, the method comprising: determining an average operating value of a condensate pump of the heat pump water heater, the condensate pump being in fluid communication with a condensate collection tray for discharging condensate collected from the evaporator of the heat pump water heater; determining a temperature of the environment; determining, based on the average operating value and the temperature of the environment, the relative humidity of the environment; and adjusting an operating parameter of the heat pump water heater to regulate the relative humidity of the environment.
 2. The method of claim 1, wherein determining the average operating value comprises determining an operating time and a condensate pump rate of the condensate pump during a predetermined time interval.
 3. The method of claim 2, wherein the average operating value is the operating time multiplied by the condensate pump rate over the predetermined time interval.
 4. The method of claim 2, wherein the predetermined time interval is eight hours.
 5. The method of claim 1, wherein the operating parameter is a speed of the compressor of the heat pump water heater.
 6. The method of claim 1, wherein the operating parameter is a cycle time of the heat pump water heater.
 7. The method of claim 1, wherein the temperature of the environment is measured at an inlet of the evaporator.
 8. The method of claim 1, wherein the temperature of the environment is measured outside of the heat pump water heater.
 9. The method of claim 1, wherein the temperature of the environment is measured both at an inlet of the evaporator and outside of the heat pump water heater.
 10. A water heater appliance defining a vertical direction, the water heater appliance comprising: an evaporator being configured to absorb heat and produce condensate; a condensate collection tray disposed under the evaporator along the vertical direction and being configured for collecting the condensate from the evaporator; a condensate pump in fluid communication with the condensate collection tray, the condensate pump being configured for discharging the condensate from the condensate collection tray through a condensate discharge line; and a controller for controlling a relative humidity in an environment in which the water heater appliance is located, the controller being configured for: determining an average operating value of the condensate pump; determining a temperature of the environment; determining, based on the average operating value and the temperature of the environment, the relative humidity of the environment; and adjusting an operating parameter of the heat pump water heater to regulate the relative humidity of the environment.
 11. The water heater appliance of claim 10, wherein determining the average operating value comprises determining an operating time and a condensate pump rate of the condensate pump during a predetermined time interval.
 12. The water heater appliance of claim 11, wherein the average operating value is the operating time multiplied by the condensate pump rate over the predetermined time interval.
 13. The water heater appliance of claim 11, wherein the predetermined time interval is eight hours.
 14. The water heater appliance of claim 10, wherein the operating parameter is a speed of a compressor of the water heater appliance.
 15. The water heater appliance of claim 10, wherein the operating parameter is a cycle time of the water heater appliance.
 16. The water heater appliance of claim 10, wherein the temperature of the environment is measured at an inlet of the evaporator.
 17. The water heater appliance of claim 10, wherein the temperature of the environment is measured outside of the water heater appliance.
 18. The water heater appliance of claim 10, wherein the temperature of the environment is measured both at an inlet of the evaporator and outside of the water heater appliance. 